[libc-commits] [libc] [libc] Basic implementation of crt0 (PR #146863)

[Petr Hosek via libc-commits]

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@@ -0,0 +1,92 @@
+//===-- Implementation of crt for arm -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/macros/config.h"
+#include "src/stdlib/atexit.h"
+#include "src/stdlib/exit.h"
+#include "src/string/memcpy.h"
+#include "src/string/memset.h"
+#include "startup/baremetal/fini.h"
+#include "startup/baremetal/init.h"
+
+#include <stdint.h>
+
+extern "C" {
+int main(int argc, char **argv);
+void _start();
+
+// Semihosting library initialisation if applicable. Required for printf, etc.
+[[gnu::weak]] void _platform_init() {}
+
+// These symbols are provided by the linker. The exact names are not defined by
+// a standard.
+extern uintptr_t __stack;
+extern uintptr_t __data_source[];
+extern uintptr_t __data_start[];
+extern uintptr_t __data_size[];
+extern uintptr_t __bss_start[];
+extern uintptr_t __bss_size[];
+
+// Based on
+// https://developer.arm.com/documentation/107565/0101/Use-case-examples/Generic-Information/What-is-inside-a-program-image-/Vector-table
+void NMI_Handler() {}
+void HardFault_Handler() { LIBC_NAMESPACE::exit(1); }
+void MemManage_Handler() { LIBC_NAMESPACE::exit(1); }
+void BusFault_Handler() { LIBC_NAMESPACE::exit(1); }
+void UsageFault_Handler() { LIBC_NAMESPACE::exit(1); }
+void SVC_Handler() {}
+void DebugMon_Handler() {}
+void PendSV_Handler() {}
+void SysTick_Handler() {}
+
+// Architecturally the bottom 7 bits of VTOR are zero, meaning the vector table
+// has to be 128-byte aligned, however an implementation can require more bits
+// to be zero and Cortex-M23 can require up to 10, so 1024-byte align the vector
+// table.
+using HandlerType = void (*)(void);
+const HandlerType vector_table[]
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petrhosek wrote:

Since the ABI here is the section name, neither this symbol nor the handler functions above need to be `extern "C"`, rather I'd put these into an anonymous `namespace`.

https://github.com/llvm/llvm-project/pull/146863